1. Field Of The Invention
The present invention is related to the field of variable volume combustion chamber internal combustion engine control systems in general and in particular to that portion of the above noted field concerned with closed loop control system. In greater detail, the present invention is concerned with a closed loop control system in which the exhaust gases of an internal combustion engine are analyzed to indicate the ratio of the air/fuel mixture being consumed by the engine and through which signals are generated in order to modulate the fuel delivery mechanism in order to provide a predetermined air/fuel ratio mixture for the engine.
2. Description Of The Prior Art
The prior art, particularly as defined by my co-pending commonly assigned patent application Ser. No. 289,200, filed Sept. 14, 1972 and issued on June 11, 1974 as U.S. Pat. No. 3,815,561, expressly incorporated herein by reference, provided for the application of an output signal from an engine combustion quality sensor to a summing point which would compare this signal with an established reference signal to drive a comparator to switch between established high and low limits which limits were not effected by the temperature environment of the sensor or the age of the sensor. The comparator signal was then applied to a fuel delivery controller to modulate fuel delivery. However, in applying this system to the fuel control mechanism of an internal combustion engine it was found that the engine exhibited an oscillatory or limit cycling type of operation due to the hard nonlinearity of the comparator in the system. The frequency of oscillation depended upon the dynamics of the engine and was normally a small fraction of the triggering frequency of the associated fuel injection system. The magnitude of the oscillation was dependent upon the open loop gain (K) of the system. The transient response time of the system was also dependent on this gain.
These two factors are diametrically opposed since a large gain will result in a fast response time but will also cause a large amplitude limit cycle while a small gain will reduce the limit cycle amplitude but system response time will be sluggish. It is therefore an object of the present invention to provide a closed loop control for an internal combustion engine, responsive to a signal indicative of the quality of the combustion process occurring within the engine and operative to maintain the quality of the combustion process at or near a desired level by exhibiting a fast response time to deviations in the quality of the combustion process while maintaining the quality of the combustion process near the desired level by exhibiting a lower limit cycle amplitude. In the application of this type of closed loop control system to an internal combustion engine as a means of controlling the amount of pollutants generated by the engine, fast response time is at a premium but the large amplitude limit cycle which accompanied a fast response time resulted in a prior art system which was constantly hunting, over a wide region, for the proper level of signal output. Thus, the system did not result in the degree of pollution control desired. It is therefore an object of the present invention to improve the above described system to reduce the amplitude of the limit cycle while retaining a fast response time. It is a further object of the present invention to provide a system with a fuel controller input signal having a "softened" nonlinearity.